This project examines the function of the caudal-related homeobox genes, Cdx1 and Cdx2, on the differentiation and development of the intestinal epithelium. The alimentary tract develops from the primitive gut tube of endoderm surrounded by mesoderm. The caudal-related transcription factors Cdx1 and Cdx2 are expressed in the endoderm of the developing intestine and are candidates for directing intestinal epithelial development and differentiation. Expression of Cdx genes during development is more complex then originally reported and knockout mouse experiments have only partially defined their function. Additionally, experiments in cell lines have defined a number of functions for Cdx1 and Cdx2, however their function in the intact intestine is not well defined. We hypothesize that Cdx1 and Cdx2 direct patterning in the developing intestinal epithelium and are important for maintenance of differentiation and the architecture and function of the fully developed epithelium. This proposal describes two inter-related Specific Aims that employ mouse models to explore the function of Cdx1 and Cdx2 in the intestine. In Specific Aim 1 loss-of-function experiments in mice will be used to determine the functional consequences of the loss of expression of Cdx1 and Cdx2 in the developing intestinal epithelium. Tissue specific gene targeting will be used to create mice with knockouts of Cdx1, Cdx2 and both genes, specifically in the intestinal endoderm and epithelium. In Specific Aim 2 both genes will be miss-expressed by creating a transgene with Cdx1 and Cdx2 under the control of the cis-regulatory elements of the winged helix transcription factor HNF3gamma. This transgene will direct expression of Cdx1 and Cdx2 in an altered pattern from the endogenous gene. Analysis of the mouse models from both Specific Aims 1 and 2 will focus on the phenotype of the gut epithelium and gene expression profiling using a panel of genes that are differentially expressed along the vertical and horizontal axes of the gut. Analysis of these mouse models will also center on alterations in development and growth as it relates to nutrition and metabolism. This project emphasizes the role of Cdx genes in gut development and differentiation, as well as the nutritional and metabolic consequences to intestinal epithelial function.